1. Field of the Invention
This invention relates to a multi-track head and more particularly to a multi-track head having at least three conversion elements formed on a common substrate.
2. Description of the Related Art
The thin-film magnetic head is manufactured by a thin-film deposition method and photo-lithography like the manufacturing process for the semiconductor IC. The head is small in size, light in weight and suited for mass production. In addition to these merits, it permits easy construction of a multi-track head which has many magnetic gaps integrated within one and the same head chip.
It is now expected that a multi-track thin-film head having more than 20 magnetic gaps integrated at a pitch of 80 .mu.m will become practicable, for example, for a digital audio tape (DAT for short) recorder which performs magnetic recording and reproduction by converting an audio signal into a digital signal. For a magnetic tape device which is used as the external storage device of a computer system, a thin-film magnetic head of 18 tracks has already been developed. A magnetic tape measuring 0.15 to 0.5 inches in width is used as a recording medium for these magnetic tape recorders. FIG. 1 of the accompanying drawings shows a typical structural arrangement of the multi-track, thin-film tape recorder.
FIG. 1 shows the head as having an n number of magnetic gaps with the middle part of the head omitted from the illustration. A reference numeral 1 denotes the substrate of the head. In this case the substrate is made of a magnetic material. There are provided an n number of magneto-electric/electro-magnetic conversion elements E1 to En (hereinafter referred to simply as conversion elements). Each of these elements is composed of an upper magnetic core 4 which is arranged to form a magnetic gap between the substrate 1 and the core and a coil 5 which is made of a thin metal film. The conversion elements which are disposed on the substrate 1 are covered with a reinforcement plate 2 which is made of a ceramic material and is indicated by broken lines.
Referring further to FIG. 1, each of the magnetic gaps 3 which is formed between the substrate 1 and the upper magnetic core 4 has a gap depth 6 extending from a sliding face 10 shown in the upper part of the drawing. To ensure adequate contact of the conversion elements E1 to En with the magnetic tape, the sliding face 10 is formed linearly in the direction Y of the conversion element alignment (in the direction of track width) and to be in a smooth approximately cylindrical surface in the traveling direction X (or X') of the tape.
The conversion elements are aligned in the direction Y. Therefore, the gap depth 6 is uniformly obtained for all the elements.
As for the magnetic recording medium, a floppy disc or the like having a circular disc shape has recently come to be used as well as the tape. For the recording medium of the disc type, the thin-film, multi-track head is arranged as shown in FIG. 2.
FIG. 2 shows the structural arrangement of a thin-film magnetic head of a two track type for use in an electronic still camera. In FIG. 2, the multi-track thin-film head 7 has two conversion elements aligned perpendicular to the surface of the paper as viewed on the drawing. Magnetic recording or reproduction is performed with the head allowed to slide over a magnetic disc 9 which is driven to rotate in the direction of arrow X. In performing the magnetic recording or reproduction, the magnetic disc is sandwiched in between the magnetic head 7 and a pad 8. The pad 8 is provided for the purpose of suppressing the rotatory vibrations of the magnetic disc 9. The pad 8 has a recessed part 8a formed on one side opposed to the magnetic head 7. The sliding face of the magnetic head 7 is arranged to slightly protrude inside the recessed part 8a. The arrangement is such that the head 7 can be brought into adequate contact with the magnetic disc 9 by utilizing air pressure developed within the recessed part 8a in conjunction with the elasticity of the magnetic disc 9. The external shape of the magnetic head 7 of FIG. 2 is as shown in FIG. 3.
In FIG. 3, a reference numeral 1 denotes a substrate like that shown in FIG. 1. Although they are not shown, conversion elements for two tracks are arranged on this substrate 1 in about the same manner as in the case of FIG. 1. The conversion elements are covered with a reinforcement plate 2. The sliding faces 10 of the substrate 1 and the reinforcement plate 2 are curved both in the direction Y of the track width and the traveling direction X of the recording medium, that is, they are formed in a spherical (convex) shape. This is because the magnetic disc deforms in both the track-width direction (arrow Y) and the traveling direction (arrow X) of the disc. Generally, in the case of the head of FIG. 3, the contact of the head with the disc (hereinafter will be called "head touch") can be adequately obtained for the two tracks with the curved surfaces symmetrically formed both in the directions of arrows X and Y. The radius of the curved surface is generally set at 5 to 20 mm although it depends on the shape of the pad 8.
The multi-track thin-film head for a magnetic disc of the type as shown in FIGS. 2 and 3 is generally arranged for two tracks. However, to meet a recently increased demand for a higher image quality, the amount of information to be handled by the head of the electronic still video cameras or the like is trending upward. A demand for a higher speed is naturally also increasing for transmission of recording and reproduced signals. This tendency is seen not only in the field of image processing apparatuses but also in the case of external memory devices of computers.
The amount of information handleable by the apparatus of the kind using a magnetic disc can be increased by increasing the number of channels also in accordance with such a structural arrangement as the one shown in FIG. 1. However, the use of a rotating medium such as a magnetic disc as in the case of FIGS. 2 and 3 necessitates the sliding face to be formed in a shape curved also in the direction of track width. This presents no serious problem so long as the number of tracks does not exceed two or thereabout as in the past. However, in order to have a greater number of channels (tracks), there arises the following problem:
For example, assuming that the head is provided with many (n number of) conversion elements E1 to En as shown in FIG. 1 and that the head is machined to have the curved face also in the direction of track width as shown in FIG. 3, if these elements E1 to En are aligned in the same manner as shown in FIG. 1, the gap depth 6 increases in the middle part of the head and decreases accordingly as it is nearer to the end part of the head. The magnetic field generating efficiency of the head depends on the size of the gap depth. The efficiency becomes lower for the middle track than for peripheral tracks. Besides, thickness of the magnetic core of the thin-film magnetic head is only between a value less than 1 .mu.m and scores of .mu.m. Therefore, in order to ensure a sufficient degree of head efficiency, the gap depth must be within a range from a value less than 1 .mu.m to 10 .mu.m at the most. The machining precision required is in the order of 1 .mu.m or less. The characteristic of the head is greatly affected even by a slight deviation from the required dimension.